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Use of NIR spectroscopy for the determination of internal quality of entire apples

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(1)

Calibration

Validation

Criteria

Units

:\lIn-:\lax

:\Iean

SD

n

SEC

SD/SEC

n

SEP

SD/SEP

Vitamin C

mg/IOOg DM 0.17 - 75.0

13.5

12.4

800

3.4

3.7

295

4.9

2.0

POQ'phenol

J.lglg

276 - 7300

1186

720

2000

178

4.1

6"-

~J

140

5.1

Brlx

0

brix

7.2 - 20.9

12.3

1.6

1000

0.45

3.6

853

0.37

4.3

lASe

of

N IR

s;peckyos.c,lYpkj

fOY

tVie ~eteYV\A,tv\'/Attov\'

of

tV\,teYV\,/AL

q u/ALttkj of

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/AppLes.

G. Sinnaeve', J.A. Fermindez Pierna', G. Lognay2, A. Rondia', P. Dupont', T. Donis', V. Baeten'", A. Mouteau', J-M Romn.;.,' and M Lateur'

IWaIloon Agricultural Research Centre (CRA-W), Quality of Agricultural products Departrnen~ Chaussee de Narnur 24, 5030; Gembloux, Belgium 2FUSAGx, Faculte Universitaire des Sciences agronomiques, Gembloux 5030. Belgium

*E-mail: baeten@cra.waUonie.be

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This work is perfonn in the framework of the HiDRAS program (High

-

Quality Disease Resistant Apples for a Sustainable agriculture). The aim is to build up a specific apple data base which should allow the breeders to make a much better use ofthe tremendous diversity conserved in many European Genetic Resources collections.

The present work investigated the use of NIR to assess the internal quality of apples by detennining Vitamin C, total polyphenol and sugar contents (brix).

MClteriCll Cl~~ V1A.et~o~5

Samples

In this study, a large amount of

apple

samples

(n= 2500)

were

collected

to

cover

a

broad

variability

including

several

varieties and cultivars harvested

between

2004

and 2007. Figure I

presents the PCA analysis showing

the homogenous distribution of the

samples.

Data acquisition

The spectra were acquired

by a FOSS NIRSystems

6500

scanning

monochromator

(400-2500,

2 nm) with the DCA

module (Direct Contact Analysis) (figure 3). The instrument is

placed upside down in order to place the iTuit directly on the

detector's window. To integrate the variability of the iTuit, 4

measurements have been perfonned by rotating the apple.

'1.'11 1.18 I."~:'><,'::.,/~ UII UI tJ

'~

)

' ,

,,-.

.

'

'-Figure 1 -Apple spectra: Principal Component Analysis

Wet chemistl.y

Concerning the reference values, the content of vitamin C was detennined by HPLC (figure 2), the total polyphenol content was obtained by the Folin-Ciocalteau method and the sugar content was obtained on the basis of a polarimetric Brix

determination.

i""

I.

t

Figure 3- FOSS-MIISystems 6500 with Direct ConJent Analysis

Data teatlnent

The Winisi III package was used for preparing the spectra and for the exploratory analysis by Principal Component Analysis (PC A). Calibration models have been developed by using the Least Squares Support Vector Machine (LS-SVM) algorithm built in a Matlab environment (Matlab 7.5,0 R200Th). The database has been split into calibration and test sets. The LS-SVM models have been constructed using the calibration set and validated using the test set.

Figure 2 - DistribuJion of vitamin C

R.t5ults

CI~~ ~t5CU55W~

The best results have been obtained with a Savitsky-Golay first derivative (9,2,1) as preprocessing. The accuracy obtained with the LS

-

SVM

regression technique (see table I) allows a good estimate of the internal quality of entire apples. Figure 4 shows the scatter plots obtained on

the validation sets for the criteria under investigation.

Table 1 - Characteristics of the apple doJa base and performances of the LS

-

SVM models

n 295 60~ ~p ~:9 SOISEP201 n 671 RZ 0.94 SEP 140 SI:lISEP 51

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1000 1500 ]((I) :MOO bOO

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Figure 4

-

Scatter plots obtained for the criteria under investigatiolt

- The

achieved results indicate that NIR could be used in breeding programs to assess the internal quality of entire apples.

- Although the vitamin C content is rather low, as it is concentrated in the outer layer of the iTuits, NIR in reflectance mode can be used to have an estimate of low concentration levels of Vitamin C.

- The total polyphenols determined by the Folin-Ciocalteau method can be predicted by NIR

-

The sugar content can also be determined by predicting the Brix of entire iTuits

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Table 1 - Characteristics of the apple doJa base and performances of the LS - SVM models

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